Alignment of an optic or electronic component

ABSTRACT

A method and an arrangement for aligning at least one optic and/or electronic component on a substrate or a corresponding support structure, wherein the method includes: arranging a hole in the support structure; arranging at least three stud bumps on the surface of the component; and arranging said stud bumps along the periphery of the hole for alignment of the component to the hole.

The present invention relates to a method for aligning an optic orelectronic component, and especially for aligning an optic fibre and anoptoelectronic component mounted on a substrate. The present inventionrelates also to an arrangement for aligning an optic or electroniccomponent, and especially for aligning an optic fibre and anoptoelectronic device mounted on a substrate.

In optoelectronic applications transceivers mounted on a substrate, suchas a low or high temperature cofired ceramic (LTCC, HTCC) substrate, areused to convert electrical signals to optical signals and vice versa.Optic fibres transmit the optic signals. The fibres have to be alignedprecisely with the transceivers in order to make a proper connectionbetween the optic fibre and the transceiver.

U.S. Pat. No. B1-6,217,232 discloses a method and apparatus for couplingan optic fibre to the output of an side emitting optoelectronic device.The optoelectronic device is mounted on a substrate and aligned with theoptical axis of the optic fibre by using posts formed on either thesubstrate or the optoelectronic device and matching resesses formed onthe other. Three or more posts and recesses will be formed on themounting surfaces so as to provide only one possible alignment. Theoptic fibre is arranged parallel with the substrate plane in a V-shapedchannel formed on the substrate and being capable of retaining the opticfibre in a predetermined alignment relative to the optoelectronic devicealigned by posts and recesses.

Forming the V-shape groove and the posts and recesses are generallyperformed by different processes which may cause alignment errorsbetween the V-shape groove and the posts and recesses. Especially whenthe V-shape groove has a relatively large width and a depth thealignment error increases and the coupling between the optoelectronicdevice and the optic fiber is poor. Further, prior art alignment methodsare relatively labor intensive and costly.

The object of the present invention is to eliminate the disadvantages ofthe prior art and to provide a new method for mounting an optic orelectronic component on a substrate and especially aligning an opticfibre with the component with improved aligning accuracy. The object ofthe present invention is also to provide a new arrangement for mountingan optic or electronic component on a substrate and especially aligningan optic fibre with the component with improved aligning accuracy.

In the present invention the component is aligned on a substrate andespecially an optical fibre is aligned with the component, for examplean optical surface emitting light source chip component, such as RCLEDor VCSEL, by using stud bumps made on the chip top metallization. Thestud bumps are manufactured with a wire bonding method and act as amechanical structure, but also as an electrical contact especially tothe substrate metallization. In the present invention, the outersurfaces of the stud bumps formed on the component are used to align thecomponent with an opening in the substrate or a corresponding supportstructure. Additionally the inner surfaces of the stud bumps may be usedto align an optic or optoelectronic element to the component.Characteristic features of the present invention are in detail presentedin the enclosed claims.

In the present invention, the optic or electronic component and also theoptical fibre are aligned mechanically and accurately. Further, aligningcan be performed by using same stud bumps for aligning both thecomponent on a substrate and the optical fibre with the component. Thisallows for low manufacturing cost. Further, the optical fibre becomesalmost in contact with the light source, which improves coupling. Themultilayer ceramic technology enables the manufacture of light emitterarrays and the integration of the controller electronics on the samemodule.

In the following, the invention will be described in more detail withreference to the enclosed drawing, in which

FIG. 1 presents passive alignment of an optic fibre with a light sourceof a RCLED according to the present invention,

FIG. 2 presents a RCLED bumping for passive alignment in FIG. 1,

FIG. 3 a presents a stud bump made with a gold wire, and

FIG. 3 b presents a top view of a stud bump of FIG. 3 a.

FIG. 1 presents aligning an optic fibre 1 to a resonant cavity LED chip2 and the latter on a substrate 3. The LED 2 is mounted on a bottom sideof the substrate 3

In the present invention the resonant cavity LED component 2 is alignedon the substrate and the optic fibre 1 is aligned to the LED 2 by usingfor example four stud bumps 5 made on the chip top metallization 22(FIG. 2) facing the substrate by using a wire bonder and arrangedsymmetrically along the periphery of the bottom opening of the hole 4 toprovide only one possible alignment. The stud bumps 5 act as amechanical structure for the LED 2 and fibre 1 alignment, but also as anelectrical contact to the substrate metallization.

The substrate consists of three dielectric layers, bottom layer 31,center layer 32 and top layer 33. The thickness of the layers istypically for example 200 μm. The substrate 3 may be either with lowtemperature or high temperature cofired ceramic (LTCC, HTCC).

The optical fibre 1 is mounted perpendicular to the plane of thesubstrate 3 through a hole 4 in the substrate 3 and aligned to the LED2. The hole 42 through tape layers 32 and 33 is slightly bigger indiameter than the fibre diameter. The bottom dielectric layer 31 has abigger hole 41, and a metallization 6 on the hole walls, to center thechip component 2 using the stud bumps 5.

The stud bumps 5 are formed by using a ball bonding apparatus accordingto following steps: a) A small ball is formed at the end of the wire,for example Au wire, passing through a bonding tool. b) The bonding toolis caused to press the small ball against the electrode for bondingthereto and forming the stud bump. c) The bonding tool is movedvertically from the surface of the electrode so that the Au wire is cutfrom the stud bump.

The stud bum 5 consists for example of a broad bottom part 51 withrounded walls 52, a conical middle part 53 with downwards sloping walls54 and an narrow upper part 55 with rounded end portion 56. There aresmall horizontal brims 57, 58 between the different parts (FIGS. 3 a and3 b).

In the assembly, the light source chip 2, equipped with stud bumps 5with bottom parts against the surface of the chip, is mounted first tothe substrate 3 by using the outer parts of surfaces 52 of the bottomparts 51 of the stud bumps for mechanical centering.

The optical fibre 1 is led through the substrate 3 and aligned to thechip 2 provided with metallization 21 on the surface facing thesubstrate by arranging the fibre between the stud bumps and by using theconical shape of the inner surfaces of stud bumps located symmetricallyon four sides of the radiating source 22, as shown in FIG. 2, so thatthe fibre 1 end finally is supported by the brims 57. The shape of thebumps can be further developed for maximum alignment accuracy by properbonding tool design and by the optimisation of the bonding parameters.

A conductive adhesive 7 a can be used on the stud bump 5 outer surfacesto accomplish an electrical connection to the metallization 6, ifnecessary. A non-conductive adhesive 7 b is used at the chip edges toattach it firmly to the substrate 3. Typically, the other chip electrodeis wire bonded with a bond wire 8 to the substrate. Further, the fibre 1is tightened to the hole 4 with adhesive 9 in the upper opening of thehole 4.

The accuracy of the fibre 1 and chip 2 alignment is dependent on howaccurately the bumps 5 are positioned on the chip 3. The stud bump 5itself is repeatable within a few micrometers. It is, however, necessaryto center the chip within ±15 μm to enable the optical fibre alignmentand to avoid excessive bending of the fibre. The stud bump positioningaccuracy is typically ±5 μm using a standard automatic wire bonder. Thiswould mean a maximum misalignment of about 10 μm. With special bondingequipment development, the accuracy could be even better.

It is obvious to the person skilled in the art that differentembodiments of the invention are not limited to the example describedabove, but that they may be varied within the scope of the enclosedclaims. The substrate may be of another type than presented above,consisting of at least two different layers. The number of stud bumps isnot limited to four. However, there have to be at least three stud bumpsarranged symmetrically along the periphery of the bottom opening of thehole to provide only one possible alignment. Further, the optoelectroniccomponent may also be of any other surface emitting component that canbe applied in the optoelectronic telecommunication or other systems, butalso any other passive or active electronic or optic component that haveto be aligned on a substrate. And further, the sud bump may be connectedto the substrate without a conductive adhesive for example by usingdirect bonding methods, such as ultrasonic bonding or thermocompressionbonding. It is also possible to use solder stud bumps which can beconnected to the substrate with a solder connection.

1. A method for aligning at least one optic and/or electronic componenton a substrate or a corresponding support structure, characterised inthat the method comprises: arranging a hole in the support structure;arranging at least three stud bumps on the surface of the component; andarranging said stud bumps along the periphery of the hole for alignmentof the component to the hole.
 2. A method according to claim 1,characterised in that aligning the component is performed by arrangingthe outer surfaces of the stud bumps against the hole walls.
 3. A methodfor aligning at least one optic fibre and an optoelectronic component toeach other according to claim 1, wherein the component is mounted on asupporting structure and the optic fibre is connected to theoptoelectronic component, characterised in that the method comprises:threading the optic fibre through the hole, and aligning the optic fibreand the component with each other by means of the stud bumps.
 4. Amethod according to claim 1; characterised in that aligning the fibre isperformed by arranging the fibre against the inner surfaces of the studbumps.
 5. A method according to claim 1, characterised in that the studbumps have at least partly a conical and/or rounded surfaces, and thataligning the optic fibre with the component is performed by adapting theoptic fibre along sloping conical inner surfaces and a horizontal brimin the stud bumps.
 6. A method according to claim 1, characterised inthat the component is a surface emitting optoelectronic component, thatthe optic fibre is arranged perpendicular to the support structure, andthat the fibre is connected to a radiating source on the metallizedsurface of the component facing the substrate.
 7. A method according toclaim 1, characterised in that a conductive adhesive is used on the studbump outer surfaces to accomplish an electrical connection to thesupport structure.
 8. A method according to claim 1, characterised inthat a direct bonding method is used to connect the stud bumps to thesupport structure.
 9. A method according to claim 1, characterised inthat the stud bumps are of a solder material, and that a solderconnection is used to connect the stud bumps to the support structure.10. An arrangement for aligning at least one optic and/or electroniccomponent on a substrate or a corresponding support structure,characterised in that the arrangement comprises: a hole in the supportstructure; at least three stud bumps arranged on the surface of thecomponent along the periphery of the hole, for aligning the componentcentered to the hole.
 11. A arrangement according to claim 10,characterised in that the stud bumps have at least partly a conicaland/or rounded surfaces, and that an optic fibre is aligned with thecomponent by adapting the optic fibre along sloping conical innersurfaces and against a horizontal brim in the stud bumps.
 12. Anarrangement according to claim 10, characterised in that the componentis a surface emitting optoelectronic component, that the optic fibre isarranged perpendicular to the substrate, and that the fibre is connectedto a radiating source on the metallized surface of the component facingthe substrate.
 13. An arrangement according to claim 10, characterisedin that a conductive adhesive is used on the stud bump outer surfaces toaccomplish an electrical connection to the substrate.
 14. An arrangementaccording to claim 10, characterised in that direct bonding is used toconnect the stud bumps to the substrate.
 15. An arrangement according toclaim 10, characterised in that the stud bumps are of a solder material,and that a solder connection is used to connect the stud bumps to thesubstrate.
 16. An arrangement according to claim 10, characterised inthat the substrate consists of at least two layers, and that thediameter of the hole portion(s) in the layer(s) near the component isbigger having place for both the stud bumps and the optic fibre than inother opening portion(s) having a diameter essentially corresponding thediameter of the optic fibre.